1. Field of the Invention
The present invention relates generally to a method of and an apparatus for sintering ceramic formed bodies, and more particularly, to a sintering method and a sintering apparatus which allow atmospheric gas to be controlled reliably and efficiently.
2. Description of the Prior Art
In mass produced ceramic electronic components and the like, a large number of ceramic formed bodies are usually sintered at the same time. For sintering such a large number of ceramic formed bodies, a tunnel furnace and a batch type sintering furnace are generally used. The tunnel furnace is used for sintering ceramic formed bodies which can be sintered according to a relatively simple temperature profile and requires little atmospheric control. On the other hand, the batch type sintering furnace is used for sintering ceramic formed bodies which require special atmospheric control.
Even when ceramic formed bodies are sintered using either one of the above described sintering furnaces, a large number of ceramic formed bodies are usually piled on a bottom board 1 as shown in FIG. 2A or in a container for sintering 3 as shown in FIG. 2B, and the bottom board 1 or the container for sintering 3 is disposed in the sintering furnace. In addition, a plurality of bottom boards 1 are usually piled upon each other and a large number of ceramic formed bodies (a lump of a large number of ceramic formed bodies is indicated by oblique hatching and designated by reference numeral 2) are disposed on each of the bottom boards 1, as shown in FIG. 2A, so as to enhance mass productivity. Similarly, a plurality of containers for sintering 3 are piled upon each other and are put into the sintering furnace, as shown in FIG. 2B, thereby to enhance mass productivity.
Meanwhile, although the bottom boards 1 or the containers for sintering 3 are disposed in the above-described sintering furnace when special atmospheric control at the time of sintering is required, atmospheric gas must be uniformly supplied to spaces between a large number of ceramic formed bodies. In addition, gas exchange on the surface of each of the ceramic formed bodies must smoothly progress. Accordingly, the gas must be uniformly discharged from the spaces between the ceramic formed bodies. In the method in which the plurality of bottom boards 1 are piled upon each other as shown in FIG. 2A, therefore, the bottom boards 1 are separated from each other by supports 4, thereby to smoothly supply the atmospheric gas to the ceramic formed bodies. On the other hand, in the structure in which the containers for sintering 3 are piled as shown in FIG. 2B, notches 3a for smoothly introducing the atmospheric gas are formed in the upper part of each of the containers for sintering 3.
In the above described sintering method using the bottom boards 1 or the containers for sintering 3, the atmospheric gas is smoothly introduced into spaces formed between the bottom boards 1 and the containers for sintering 3. However, it is difficult to cause the atmospheric gas to uniformly spread over the large number of piled ceramic formed bodies.
More specifically, as shown in a cross sectional view of FIG. 3, atmospheric gas introduced into a lump 2 of a large number of ceramic formed bodies is smoothly supplied to ceramic formed bodies located in a portion (a portion indicated by an arrow A) in the vicinity of the surface of the lump 2 of the ceramic formed bodies, while not easily spread over ceramic formed bodies located in a portion indicated by an arrow B, that is, ceramic formed bodies located in a lower central part of the lump 2.
Furthermore, it is difficult to uniformly discharge gas after being subjected to gas exchange on the surface of each of the ceramic formed bodies in the lump 2. That is, the gas is smoothly discharged from spaces between the ceramic formed bodies located in the portion indicated by the arrow A in the vicinity of the surface of the lump 2, while the discharging speed of the gas from spaces between the ceramic formed bodies located in the portion indicated by the arrow B is significantly lower.
As described above, in the conventional sintering method using the bottom boards 1 or the containers for sintering 3, there arises a difference in atmosphere given between the ceramic formed bodies located in the vicinity of the surface of the lump 2 of the piled ceramic formed bodies and the ceramic formed bodies located in the inner part thereof. As a result, a sintered body which is not sufficiently sintered, a sintered body in which holes remain and a sintered body whose electrical characteristics are degraded are liable to be formed.